(1) Field of the Invention
The invention concerns a flexible response secured mechanical balancing device for a multiple fluid-pressure control actuators system in a vehicle.
(2) Description of Related Art
The most general technical domain of the invention is the one of fluid-pressure actuators, e.g. of the hydraulic type, for displacing one or a plurality of output members between two extreme positions. Depending on applications, this displacement is either linear or rotational.
The invention concerns multiple fluid-pressure actuators, i.e. wherein a plurality of fluid-pressure actuators cooperate together so as to produce a power force capable of displacing a set of output members, either with a linear motion or rotational motion.
As exposed further on, the invention specifically relates to such multiple fluid-pressure actuators which are distinct one with the other, placed in series one relative the other and having a plurality of mechanically linked output members, i.e. common output members that are movable together as a single unitary set.
The common output members of a single actuating system behave as a unique output organ, so that any identical control movements at one common output member provokes the same control movement at each other common output member in the same actuating system.
In examples of the invention, these common output members are dedicated to control systems in vehicles like aircrafts. For instance, these control systems are flight controls for displacing between two extreme positions one or a plurality of aerodynamic arrangements of e.g. flying-control surfaces, lift-increasing flaps, air brakes, spoilers, flaps or the like, through operation of the fluid-pressure actuators.
The invention is also useful in the field of rotary wing aircrafts, where the safety and weight requirements are especially drastic.
The invention responds to several technical problems.
In vehicles like aircrafts having control systems with multiple fluid-pressure actuators, a technical problem is mentioned as “Avoiding Force Fight”. When a multiple fluid-pressure actuator is providing power to offer motion to a given aircraft control system, it is needed to ensure a convenient mitigation of force fight between each of the cooperating fluid-pressure actuators which are coupled to a set of common mechanical output members and which are powered by at least two independent fluid-pressure networks.
In an aircraft control system of the type aimed by the invention, the plural independent fluid-pressure networks (each having e.g. tanks, circuitry, pumps and valves, etc.) are arranged to be able to produce continuously, simultaneously and cooperatively the fluid-pressure power generating the aimed location/positioning movement of the common output members of the actuators: this is called an “active-active” operation mode.
In theory, the active-active operational mode does present the potential for a resultant force fight between the active actuators controlling the common output members. The force-fight results from the fact that the actuator components—in all the involved independent fluid-pressure networks—have distinct and unique tolerances. The term tolerance means here positional, shape and dimensional actual characteristics.
The installation and component position adjustment optimizing reduces some of the differences between coupled independent fluid-pressure networks. Although, the still existing differences as well as further shifts during operation, e.g. due to wear, can result in one independent fluid-pressure network to attempt to position one of the common output members towards a different location than the position attempted by another independent fluid-pressure network.
The resulting effect is differential fluid-pressure development in the extension/retraction chambers of the cooperating actuators, causing in antagonistic force or torsion moment (torque) development on the common output members. This is because the fluid pressure in the actuators competes with each other to displace the common output members to different positions/locations, while they are linked together mechanically.
This differential and antagonistic force or torsion moment introduces stress to the common parts of the actuators and do result in a fatigue load accumulation.
This problem could be summed up in balancing the relative pressure in the separate fluid-pressure independent network, so as to avoid deleterious stress and constraints within a control actuator for an aircraft.
So as to obtain such balancing, it has been proposed to make use of electronic devices. Any solution to reduce force fight by the usage of electronic balancing devices does need a complex electric and electronic environment to interface with the balancing means controlling the relative fluid-pressure. For instance, such an electronic environment is of a fly-by-wire architecture.
In some types of aircrafts, such electronic balancing devices cannot be used due to the electronic environment (e.g. existing/basic architecture) for the aircraft that cannot provide a convenient interface. A convenient electronic architecture, i.e. compatible with nowadays electronic balancing devices, may neither exist onboard and/or be compatible with a given aircraft.
The alternative to electronic balancing devices is usually called a mechanical balancing device. Such mechanical balancing devices generally provide spring loaded relief valve function, integrated into by-pass valves. This is realized in actual design e.g. in the 4-axis actuator of the TIGER® helicopter (Cf. e.g.: http://www.liebherr.com/AE/en-GB/126883.wfw?file=˜%2FCMS%2Fdownloads%2FBP_Helicopter_20s_enGB_04.pdf).
Another problem is related to existing mechanical balancing devices. In some available mechanical balancing devices, having a spring loaded relief valve function integrated into by-pass valves, the mechanical balancing device can only provide a monolithic relief against a single pre-determined level of pressure, defined by the mechanic characteristics of the relevant spring.
This technical problem is the limitation to monolithic relief against a single level of pressure, while flexible/adaptive relief against a plurality of occurring levels of pressure would be useful for enhancing the precision, safety maneuverability of the aircraft equipped with (a) mechanical balancing device(s).
Therefore, a flexible (i.e. adaptive or variable) balancing of different pressure levels, creating forces below/above a pre-determined/single spring force, is not available with present mechanical balancing devices.
A further problem relates to some operation modes. In an aircraft control system of the type concerned by the invention, the multiple independent fluid-pressure networks are arranged to produce continuously, simultaneously and cooperatively the control power generating the aimed position/movement in the common output member: this is the “active-active” operation mode. Other “active-passive” operation modes have to be provided, that should meet the pre-requisites for safe operation required by airworthiness regulations.
In some aircraft control systems having a mechanical balancing device, should an “active-passive” operation mode be implemented, this would render the active pressure impossible to be used by the actuator. Such prior art mechanical balancing devices does allow a multi located pressure balancing in the continuous “active-active” operation mode of the fluid-pressure networks. But the prior art mechanical balancing devices do not allow the “active-passive” operation modes.
In case of “active-passive” operation mode, the mechanical balancing device aims to maintain to balance the pressure of the active independent fluid-pressure network against the passive one. This would render the active pressure impossible to be used by the actuator coupled to the independent fluid-pressure networks. Consequently, these prior art devices does not meet the pre-requisites for safe operation required by airworthiness regulations.
So presently, the design of fluid-pressure actuators with common outputs has always to consider the worst-case stress and fatigue that could occur in the active-active operation mode, due to force-fight. No fail-safe mechanism for active-passive operation mode seems available.
The following prior art documents are known: EP0112624, EP1504195, U.S. Pat. No. 3,469,501, U.S. Pat. No. 4,549,977, U.S. Pat. No. 8,181,901, US2011/0109671, US2011/0251739, US2011/0108671 and US2012/241563.
The document EP0112624 describes a mechanical balancing valve to balance fluid-pressure values between two fluid networks feeding chambers. The mechanical balancing valve maintains pressures at a pre-determined pressure value in one chamber relative to another chamber. The invention takes advantage of the principles of the valve. The mechanical balancing valve has no “active-passive” operation mode. So, during such operation mode, the valve would maintain to balance the pressure of the active network against the passive one, which would render the active pressure impossible to be used by the actuator.
The document EP1504195 describes an integrated three function valve. In helicopters the three function valve aims to provide a flight critical failure mode, the helicopter having a fly-by-wire rotor control, a triple redundancy hydraulic system and linear variable transducers connected to an actuator.
The document U.S. Pat. No. 3,469,501 describes a by-pass for aircraft control surfaces. The control surfaces are piloted by hydraulic actuators cylinders. A plunger operates a three ways operated valve to close a port or leave it open.
The document U.S. Pat. No. 4,549,977 describes another principle of mechanical balancing valve maintaining pre-determined pressure values, from which invention takes advantage of. The mechanical balancing valve allows a kind of flexible pressure balancing in continuous “active-active” mode of the hydraulic networks, but do not cover the “active-passive” operation mode.
The document U.S. Pat. No. 8,181,901 describes a hybrid helicopter having a rotor and propellers both driven when required by a mechanical interconnection. Second means control e.g. pitch of the rotor or lift-producing/stabilizer surfaces.
The document US2011/0109671 describes electronic force fight compensation that addresses the monitoring of differential chamber pressures. The electronic force fight compensation use pressure sensors and monitoring logics to provide individual actuator control thus balancing out differential chamber pressures.
The document US2011/0251739 describes a distributed flight control fly-by-wire linked to a pair of pilot and co-pilot control sticks. Specific functions like autopilot and programs are taking authority on stability or gust suppression.
The document US2011/0108671 describes another electronic force fight compensation addressing the monitoring of differential chamber pressures.
The document US2012/241563 describes a manual flight control in a rotary wing aircraft. Emergency piloting means have series of actuators.
Despite the valuable enhancements brought to prior art mechanical balancing devices, limits and drawbacks remain for multiple fluid-pressure control actuators system and vehicles operated thanks to such devices and systems.
In fact, there is still a need for further optimizations in order to increase the efficiency and enhance flexibility of mechanical balancing devices, while offering a fail-safe response to mechanical balancing devices controlling fluid-pressure powered actuators systems.
The advantages of the invention depart it from the prior art and provides such optimizations, flexibility and secured response.
The invention is defined by the appended claims, enhancing the prior art corresponding to the document EP0112624 or the document U.S. Pat. No. 4,549,977.
Thus, the invention allows usage of a mechanical balancing device in multiple fluid-pressure actuating systems of vehicle operating controls, flexibly responding to different fluid-pressure levels. The invention allows an automatic balancing of differential fluid-pressures values by the direct application of the fluid-pressure principle of “communicating vessels”. Therefore, adverse force fighting between cooperating fluid-pressure actuators will be avoided.
The invention further ensures that the balancing function will not cause loss of cooperating fluid-pressure actuators function in case of occurring of an “active-passive” operating mode.
The invention can be used in many fluid-pressure actuators, e.g. hydraulic, which feature a plurality of common mechanical output members. The invention can be used with such actuators of various types, e.g. provoking linear or rotating displacements of the common mechanical output members.
The invention is not depending of the overall control architecture of the actuating system (e.g. by manual input, by electronic input i.e. fly-by-wire). Though, the invention can be directly incorporated into any existing mechanical design of such actuating systems and does not require any additional external information processing means like complex control electronics architecture.
Therefore, the invention is useful by offering numerous advantages to various types of vehicles, including rotary wing aircraft, drones and/or unmanned aerial vehicles (UAV).
Some examples of objects of the invention are now summarized. These objects are detailed in the appended claims.